If you mean a politician who is an atheist, then of course. If anything, they would probably make a better politician than a religious person because they're unlikely to be biased.

If you mean not believing in politics or politicians...well I think even if we don't want to admit it we all have an opinion to some degree on issues that affect us. But it's easy to lose faith in any politicians these days. And a large amount of people have become indifferent and uninterested in politics and don't even bother to vote.